Optical code division multiple access (OCDMA) systems allow multiple users to simultaneously share an optical medium, thus significantly increasing the transmission capacity of optical fibers. The attributes of OCDMA networks include multiple asynchronous access by independent users, enhanced security, and soft response to subscriber number increase.
There has been renewed interest in optical code-division-multiple-access (OCDMA) systems due to their potential for enhanced data privacy as well as for plug-and-play operation. One drawback of OCDMA, however, may be that for the kinds of data rates demanded by current practical applications, and the number of users desired to be supported, conventional 1-D OCDMA systems may require an excessively high chip rate.
One approach towards partially alleviating the high chip rate requirement has been the introduction of two dimensional (2-D) OCDMA architectures, in which the quasi-orthogonal spreading codes of the different users are spread over both time and wavelength. The spreading codes used in OCDMA systems are commonly referred to as optical orthogonal codes (OOC), and have the property that each code can be distinguished from, and detected against, any circular shift of itself and/or any other code. Even under the time/wavelength approach with a reasonable number of wavelengths and practical chipping rates, however, OCDMA systems may still be unable to accommodate a sufficient number of active users.
For these reasons, there is a need for a method and system that allows a greater spectral efficiency to be achieved in OCDMA system, so that a higher number of users can be accommodated.